[PATCH] x86_64: Fix fast check in safe_smp_processor_id

The APIC ID returned by hard_smp_processor_id can be beyond
NR_CPUS and then overflow the x86_cpu_to_apic[] array.

Add a check for overflow. If it happens then the slow loop below
will catch.

Bug pointed out by Doug Thompson

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/x86_64/kernel/smp.c b/arch/x86_64/kernel/smp.c
index fe906ba1cf45..5885b8f044b2 100644
--- a/arch/x86_64/kernel/smp.c
+++ b/arch/x86_64/kernel/smp.c
@@ -520,13 +520,13 @@ asmlinkage void smp_call_function_interrupt(void)
 
 int safe_smp_processor_id(void)
 {
-        int apicid, i;
+        unsigned apicid, i;
 
         if (disable_apic)
                 return 0;
 
         apicid = hard_smp_processor_id();
-        if (x86_cpu_to_apicid[apicid] == apicid)
+        if (apicid < NR_CPUS && x86_cpu_to_apicid[apicid] == apicid)
                 return apicid;
 
         for (i = 0; i < NR_CPUS; ++i) {